Gallery: The Physics of the Red Bull Stratos Jump
01space-jumpers-in-star-trek
What If You Jumped From the Space Station? ------------------------------------------ This is one of the basic plot points in the last Star Trek movie. James Kirk along with two others jumped out of shuttle at about the height of the International Space Station (well, they jumped onto the planet Vulcan). If they started from rest (so, not orbiting) how fast would they go? Would the g-forces kill them? The calculation would be similar to the model for the Red Bull Stratos jump. The main difference is the atmospheric model for the density of air as a function of altitude. However, when you add this data for a greater height you find that these space people reach a maximum speed of 4900 mph. Why so much faster? These space jumpers have much more time to accelerate with very little air resistance. But what happens when the get into higher density air? This is where the problem occurs. Since they are going so fast, they quickly get into a part of the atmosphere with a significant density and extremely large air resistance. This will produce an acceleration around 20 g's (for at least a short period of time). Survivable, but just barely. [Here is the post with all the details.](http://stag-komodo.wired.com/wiredscience/2010/05/star-trek-space-jump/)
02launching-of-a-test-balloon
How Big Does the Balloon Need to Be? ------------------------------------ As I said before, the key to the high speed is the low air density. However, the density of air does play an important role in the buoyancy on the balloon. How does a balloon float? The basic idea is that the air pushes more on the bottom of the balloon more than it pushes on the top. But as the density of air decreases with altitude, this upwards force from the air gets smaller. You can fix this with a bigger balloon. [The details on how big the balloon would have to be.](http://stag-komodo.wired.com/wiredscience/2010/05/how-big-of-a-balloon-do-you-need-to-get-to-120000-feet-high/) *Image: Red Bull Stratos*
03data-from-a-stratos-test-jump
If You Make a Model For the Stratos Jump, How Do You Test It? ------------------------------------------------------------- This is the fun part of physics - making models. Let's say you want to find out how fast Felix will be going at some moment. Could you just use the plain old kinematic equations? No, you can't. You can't use the kinematic equations because the forces (and thus the acceleration) is not constant. There is a trick. The trick is to break the motion into many small time intervals. If the time intervals are small enough then we can pretend like the acceleration IS constant. With every trick, there is payment. In this case by making an easier problem, we end up with many more (but easier) problems. If a human did this problem, you would hear some complaining. Computers, on the other hand, don't complain. This is the essence of a numerical model. But when you make a model, you would like to check it with real data. That is where the Red Bull Stratos test jump data comes in. By adjusting the parameters in my numerical model, I can get the real data and the computer-based data to be pretty close. [Here is the post with all the details](http://stag-komodo.wired.com/wiredscience/2012/07/analysis-of-a-red-bull-stratos-practice-jump/).
04felix-in-free-fall
How Will They Even Know How Fast He Falls? ------------------------------------------ If you want to set a record for the fastest free fall, you are going to have to measure something. Sky divers don't have a speedometer on their body to easily record things. In the case of the Red Bull Stratos jump, the data will be recorded with a Global Positioning System (GPS). Just about every smart phone has a built in GPS, but that wouldn't work here. Just about every GPS is required by the US government to not function at speeds of over 1000 knots or at an altitude of over 60,000 feet. Why? I guess because if they did work under those conditions you could make a fairly simple guided missile. Any GPS that works in this area has to be classified as "munitions". Once you have your functioning GPS, you can get position and time data for the fall. By looking at how far Felix moves in each time interval, you can also get speed values. Really, that's all they do. Of course, they had to test this to make sure the system was accurate. To do this, they dropped a test pod with the same GPS. The GPS recorded data and this is compared with data from a ground-based radar. [Here is the post with more details](http://stag-komodo.wired.com/wiredscience/2012/07/how-do-you-measure-the-stratos-space-jump/). *Image: Red Bull Stratos*
05is-this-science
How Will This Jump Help Science? -------------------------------- This is a great question. What kind of discoveries or advances in science could this jump? What technological advances will we get from this space jump? Better space suits? Better balloons? Maybe, but that's not the point. Here is where I get to use the famous Richard Feynman quote: > "Physics is like sex: sure, it may give some practical results, but that's not why we do it." The same is true with space jumps. Then WHY? The answer is simple: because it's there, because we're humans. This is what humans do. This is the major reason behind most scientists and explores. Yes, we lie. We tell the funding agencies that there will be some products from our projects. Often they will get fooled by this lie and give us money. Suckers. While I am talking about exploration, don't forget about Exploration Day. [Here is the site: Americans for Expedition Day Petition](http://explorationdayusa.org/). The basic idea is to change Columbus Day to Exploration Day. This way we can celebrate ALL explores: Christopher Columbus, Neil Armstrong, oh and Felix Baumgartner. *Image: Red Bull Stratos*
06is-the-stratos-jump-like-reentry
Will Felix Heat Up Like the Space Shuttle in Reentry? ----------------------------------------------------- Everyone has probably seen images of the Space Shuttle during reentry and everyone is aware of the importance of the heat shield tiles on the bottom. Why does the Space Shuttle get so hot? The Space Shuttle is doing two things in orbit. It is high up (about 300 km above the surface) and traveling very fast in order to stay in orbit (once around the Earth in about 90 minutes). This means that the Shuttle has both kinetic energy and gravitational potential energy. If it wants to stop on the ground, this energy has to go somewhere. Of course, the Space Shuttle accomplishes this by using the atmosphere as a type of brake. The result is a hot space shuttle. Felix is different than the Space Shuttle. He is just falling and not moving in orbit. If you look at how much energy he will have to lose to the air, it isn't all that much more than a normal sky diver. Well, it is more, but he has more time to "cool off" also. In the end, Felix won't burn up as he falls. [Here is a post with all the details.](http://blog-admin.wired.com/wiredscience/2012/02/would-the-stratos-space-jump-be-similar-to-reentry/) *Image: NASA*
07falling-faster-than-the-speed-of-sound
Can you fall faster than the speed of sound? -------------------------------------------- In short, yes. As Felix falls from a very high altitude, there are essentially two forces acting on him. There is the gravitational force pulling down and an air resistance pushing up. During the entire jump (even up to 120,000 feet) the gravitational force will be pretty constant. The air resistance force is not constant. It depends on his speed as he moves through the air. The faster he goes, the greater the air resistance force. For a normal sky diver jumping out of a plane, the jumper will fall and increase speed. However, before too long the speed will increase to a value such that the air resistance force has the same magnitude as the gravitational force. At this point, the net force on the jumper will be zero and he or she will fall at a constant speed. This speed is call the terminal velocity and has a typical value around 120 mph (around 50 m/s). There is one important difference between Felix's jump and a normal sky diver - the density of air. At 120,000 feet, the density of air is much lower than it is near the surface of the Earth. This means that the air resistance force will be much smaller at this high altitude (for the same speed) than it would be when he is lower. The result is that he will keep increasing in speed to a value much higher than 120 mph. Yes, he should go faster than the speed of sound. [Here is a post with more details and calculations](http://stag-komodo.wired.com/wiredscience/2012/02/stratos-space-jump-can-you-fall-faster-than-the-speed-of-sound/). *Image: Red Bull Stratos*
